1. Technical Field
The present disclosure relates generally to the load balancing of traffic in a network.
2. Description of the Related Art
In packet switching networks, the terms “traffic flow,” “packet flow,” “network flow,” and “flow” may be used interchangeably. The term “flow” may refer to a sequence of packets sent from a source device to a destination, which may be a destination device, a multicast group, or a broadcast domain. RFC 3697, “IPv6 Flow Label Specification,” J. Rajahalme, A. Conta, B. Carpenter, and S. Deering, March 2004, defines a flow as “a sequence of packets sent from a particular source to a particular unicast, anycast, or multicast destination that the source desires to label as a flow. A flow could consist of all packets in a specific transport connection or a media stream. However, a flow is not necessarily 1:1 mapped to a transport connection.”
RFC 3917, “Requirements for IP Flow Information Export (IPFIX),” J. Quittek, T. Zseby, B. Claise, and S. Zander, October 2004, provides that “[a]ll packets belonging to a particular flow have a set of common properties.” Often, such properties are defined by the value of one or more packet header fields, such as a source IP address field, destination IP address field, transport header field (e.g., source port number and/or destination port number), or application header field (e.g., Real-time Transport Protocol (RTP) header fields). The properties of a flow may also include one or more characteristics of the packet itself (e.g., number of MPLS labels) and/or values of one or more fields derived from packet treatment (e.g., next hop IP address, output interface, etc.) A packet is identified as belonging to a flow if it completely satisfies all the defined properties of the flow.
When a network device such as a switch or router receives a packet, the network device transmits the packet to a destination to which the packet is addressed. Often, the network device will have two or more possible paths via which the network device may transmit the packet. However, since the path selection is typically based upon packet header information identifying a flow, all packets associated with a given flow will be transmitted via the same path.